International Conference on Electrical, Electronics, and Optimization Techniques (ICEEOT) - 2016

978-1-4673-9939-5/16/$31.00 ©2016 IEEE 1

Control of Induction Motor Drive using Space Vector PWM

Mohammed abdul khader aziz biabani [Power Electronic & systems] EED Dept

Muffakham Jah College of Engineering & Technology Hyderabad, India.

azizbiabani009@gmail.com

Syed mahamood ali

[Power Electronic & systems] EED Dept Muffakham Jah College of Engineering & Technology

Hyderabad, India. Mahamood1248@gmail.com

Abstract— In this paper speed of induction motor is

controlled which is fed from three phase bridge inverter. In this paper the speed of an induction motor can be varied by varying input Voltage or frequency or both. Variable voltage and variable frequency for Adjustable Speed Drives (ASD) is invariably obtained from a three-phase Voltage Source Inverter (VSI). Voltage and frequency of inverter can be easily controlled by using PWM techniques, which is a very important aspect in the application of ASDs. A number of PWM techniques are there to obtain variable voltage and variable frequency supply such as PWM, SPWM, SVPWM to name a few, among the various modulation strategies SVPWM is one of the most efficient techniques as it has better performance and output voltage is similar to sinusoidal. In SVPWM the modulation index in linear region will also be high when compared to other

Keywords— Adjustable Speed Drive (ASD); Voltage source inverter (VSI), Sinusoidal PWM (SPWM), Space Vector PWM (SVPWM).

I. INTRODUCTION An adjustable speed drive (ASD) is a device used to provide continuous range process speed control. An ASD is capable of adjusting both speed and torque from an induction or synchronous motor. An electric ASD is an electrical system used to control motor speed. ASDs may be referred to by a variety of names, such as variable speed drives, adjustable frequency drives or variable frequency inverters. The two terms adjustable frequency drives or variable frequency inverters will only be used to refer to certain AC systems, as is often the practice, although some DC drives are also based on the principle of adjustable frequency (Switching frequency of chopper switch). Adjustable speed drives are the most efficient (98% at full load) types of drives. They are used to control the speeds of both AC and DC motors. They include variable frequency/voltage AC motor controllers for squirrel-cage motors, DC motor controllers for DC motors, eddy current clutches for AC motors (less efficient), wound-rotor motor controllers for wound-rotor AC motors (less efficient) and cycloconverters (less efficient).

Figure 1: ASD Block Diagram

A squirrel cage induction motor with constant frequency, constant magnitude voltage supply is supplied, the motor provides constant torque and speed characteristic. To regulate the speed and torque for same induction motor, the motor has to run at variable voltage and frequency. The variable voltage and variable frequency can be obtain from (ASD) adjustable speed drives. AC to DC converter is the first step by which we get DC voltage from AC utility grid. This step is called rectification it occur by diodes connected in bridge form. The second step is DC to AC by operating in inversion operation mode is called inverter device. The converter in ASD is operated in such a way that to obtained variable voltage and frequency at output of the ASD by which motor speed, torque can be controlled with high performance.

II. PULSE WIDTH MODULATION (PWM) Variable voltage and frequency supply for Adjustable Speed Drives (ASD) is invariably obtained from a three-phase VSI. In power electronics, converters and motors, the PWM technique is mostly used to supply AC current to the load by converting the DC current and it appears as a AC signal at load or can control the speed of motors that run at high speed or low. The duty cycle of a PWM signal varies through analog components, a digital microcontroller or PWM integrated circuits.

Figure 2 shows the comparator gets the inputs as reference waveform (square wave) and a carrier wave (triangular wave) is supply to the comparator to obtained PWM waveform. Triangular wave is formed by op-amp driver. Triggering

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pulses are produced at the instant of the carrier signal magnitude is greater then the reference signal magnitude. To turn-on the IGBT switches, firing pulses are produced, the output voltage during the interval triangular voltage wave stipulated the square modulating wave. Advantages of PWM technique:

• Output voltage can be controlled without other components.

• Output voltage can be controlled, lower order harmonics can be eliminated and filtering out higher order harmonics by this filter requirements is minimized.

Disadvantages of PWM technique: • The inverter switches are costly as they must have

low turn off and turn on times.

Types of PWM techniques: A number of PWM techniques are there to obtain variable voltage and frequency supply such as, (i) Single-pulse modulation (ii) Multiple-pulse modulation (iii) Selected harmonic elimination PWM (iv) Minimum ripple current PWM (v) Sinusoidal-pulse PWM (SPWM) (vi) Space vector-pulse PWM (SVPWM) i. Single Pulse Modulation: The output voltage waveform of single pulse full-bridge inverter is modulated, it contains pulse of width located symmetrically about /2 and another pulse located symmetrically about 3 /2. The range of pulse width 2d varies from 0 to ; i.e.0<2d< . The output voltage is controlled by varying the pulse width 2d. This shape of the output voltage wave is called quasi-square wave. ii. Multiple-pulse modulation: This method of pulse modulation is an extension of single-pulse modulation. In this method, several equidistant pulses per half cycle are used. iii. Selected harmonic elimination PWM:

Figure 3: Phase Voltage Wave for SHEPWM

The undesirable lower order harmonics of a square wave can be eliminated and the fundamental voltage can be controlled as well by what is known as selected harmonic elimination

(SHE) PWM. A large no. of harmonics can be eliminated if the waveform can accommodate additional notch angles. The general Fourier series of the wave can be given as

(1) Where;

For a waveform with quarter-cycle symmetry only the odd harmonics with sine components will be present. Therefore, an=0

(2) Where, Assuming that the wave has unit amplitude that is v(t)=+1, bn can be expanded and after solving we can get,

(3) iv. Minimum ripple current PWM: One disadvantage of the SHE PWM method is that the elimination of lower order harmonics considerably boosts the next higher level of harmonics. Since the harmonic loss in a machine is dictated by the RMS ripple current, it is the parameter that should be minimized instead of emphasizing the individual harmonics. v. Sinusoidal-pulse PWM (SPWM): Sinusoidal PWM is a modulation technique in which a sinusoidal signal is compared with the triangular signal, in which the frequency of triangular signal (ftri) is equals to the desired sinusoidal output and the frequency of triangular signal gives the switching frequency of the switches.

Figure 4: Output Voltage Waveform with Sinusoidal Pulse

Modulation The magnitude of o/p voltage depends on modulation index which is defined as, “the ratio Vtri/VC is called Modulation Index (Ma)” and it controls the harmonic content of the output voltage waveform.

(4) ADVANTAGES

• Controlled inverter output voltage • Reduction of harmonics

DISADVANTAGES • Increase of switching losses due to high PWM

frequency • Reduction of available voltage • EMI problems due to high-order harmonics

Space vector-pulse PWM (SVPWM): The advance method in PWM techniques is space vector PWM method. It computation intensive PWM method and is excellent method

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among all the PWM techniques for variable frequency drive application. Its characteristic’s is superior to other methods so it is wide spread application in recent years.

III. SPACE VECTOR-PULSE PWM (SVPWM)

It is an algorithm for the control of pulse width modulation (PWM). SVPWM is used for producing of alternating current (AC) waveforms. It is frequently used to drive 3-phase AC powered motors at variable speed from DC power. Various variations of SVPWM that result in different quality and computational requirements. The development is in the reduction of total harmonic distortion (THD) created by the rapid switching inherent to these algorithms.

Space vector modulation is a PWM regulator algorithm for multi-phase AC generation. The reference signal is sampled frequently, after each sample, non-zero active switching vectors adjacent to the reference vector and one or more of the zero switching vectors are preferred for the suitable fraction of the sampling period in order to integrate the reference signal as the average of the used vectors.

Principle of Space Vector PWM:

The circuit model of a typical three-phase voltage source PWM inverter is shown in Fig. 5, S1 to S6 are the six power switches that shape the output, which are controlled by the switching variables a, a , b, b , c and c . When an upper IGBT is switched on, i.e., when a, b or c is 1, the corresponding lower IGBT is switched off, i.e., the corresponding a , b or c is 0.

Figure 5: Three-phase voltage source PWM Inverter

Therefore, the ON and OFF states of the upper IGBTs S1, S3 and S5 can be used to determine the output voltage. The relationship between the switching variable vector and the line-to-line voltage vector is given by in the following:

(5)

The relationship between the switching variable vector [a,b,c]^t and the phase voltage vector [Vab Vbc Vca]^t is given by in the following:

(6)

As illustrated in Figure-5, there are eight possible combinations of ON and OFF patterns for the three upper power switches. The on and off states of the lower power devices are opposite to the upper one and so are easily determined once the states of the upper power IGBTs are determined. According to equations (5) and (6), the eight switching vectors, output line to neutral voltage (phase voltage), and output line-to-line voltages in terms of DC link Vdc, are given in Table 1, and Fig. 5 shows the eight inverter voltage vectors (V0 to V7). The major advantage of SVPWM method is from the fact that there is a degree of freedom of space vector placement in a switching cycle. This improves the harmonic performance of this method. Table 1: Switching vectors, phase voltages and output line to

line voltages

Figure 6: Basic Sector and Vector diagram.

To implement the space vector PWM, the voltage equations in the abc reference frame can be transformed into the stationary dq reference frame that consists of the horizontal (d) and vertical (q) axes.

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The relation between these two reference frames is below, (7)

(8)

(9) And f denotes either a voltage or a current variable. As described in Fig. 7, this transformation is equivalent to an orthogonal projection of [a,b,c]t onto the two-dimensional perpendicular to the vector [1,1,1] t (the equivalent d-q plane) in a three-dimensional coordinate system. As a result, six non-zero vectors and two zero vectors are possible. Six nonzero vectors (V1 - V6) shape the axes of a hexagonal as depicted in Fig. 7, and feed electric power to the load. The angle between any adjacent two nonzero vectors is 60 degrees. Meanwhile, two zero vectors (V0 and V7) are at the origin and apply zero voltage to the load. The eight vectors are called the basic space vectors and are denoted by V0, V1, V2, V3, V4, V5, V6, and V7. Steps for implementation of Space vector PWM:

Step 1: Determine Vd, Vq, Vref and angle ( )

Step 2: Determine time duration T1, T2, T0

Step 3: Determine the switching time of each IGBT (S1 to S6) Step 1: Determine Vd, Vq, Vref, and angle ( ): From Fig. 5.5, the Vd, Vq, Vref,and angle ( ) can be determined as follows:

(10)

(11)

(12)

; (13)

Where, f = fundamental frequency

Step 2: Determine time duration T1, T2, T0:

From Fig. 5.6, the switching time duration can be calculated as follows:

Switching time duration at Sector 1:

(14)

(15)

Where, (0 60)

(16)

(17)

(18)

Figure 7: Reference vector as a combination of adjacent vectors at sector 1.

Switching time duration at any Sector:

(19)

(20)

Where n= 1 trough 6, 0 60

Step 3: Determine the switching time of each IGBT (S1 to S6):

Following figure gives the switching times of each IGBT switches. Here Fig. 8 gives the brief idea about the switching timing pattern of inverter IGBT switches under different sectors to generate three phase voltage waveform.

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Figure 8: Switching pulse pattern for the three phases in Sector 1.

Based on above figure, the switching time at each sector is summarized in Table (2), and it will be built in Simulink model to implement SVPWM.

Table 2: Switching time calculation at each sector

IV. SIMULATIONS AND RESULTS Simulation of sinusoidal PWM based model: In Sinusoidal PWM three phase reference modulating signals are compared against a common triangular carrier to generate the PWM signals for the three phases. It is simple and linear between 0% and 78.5% of six step voltage values, which results in poor voltage utilization. Frequency in conventional SPWM output waves owing to their fixed switching frequencies.

Figure 9: SPWM Pulses The simulation circuit connection of a three phase inverter based induction motor drive with Sinusoidal PWM (SPWM) is as shown in above figure. Here the three-phase 415V, 50Hz ac supply is converted into dc and then this DC voltage is converted into 3-phase variable frequency ac. Here the controlling of inverter is done by PWM method i.e. sinusoidal PWM. The speed and electromagnetic responses of induction motor with the different load torques at different instants are as shown in Fig. 11. From this figure it is observed that when load is applied on the motor the speed of motor gets reduced.

Figure 10: Inverter o/p line voltages

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Figure 11: Motor Speed and Electromagnetic torque.

Simulation of Space Vector PWM based model:

i) Open Loop Model:

SVPWM based pulse generator simulation diagram is as shown in Fig. 14. The switching times of switches T1, T3 and T5 are determines in the block MATLAB function block to which some parameters are given such as sector number, angle ( ), Vref and sampling time. The switching times T1, T3 and T5 are calculated in 6 sectors individually by changing the sector. The output of the block is T1, T3 and T5 which is again compared with the high frequency carrier wave so as to reduce the harmonics in the output of inverter. And T4, T6 and T2 are the inverted switching times of T1, T3 and T5 respectively.

T1 to T6 pulse signals are as shown in Fig. 12. These pulsed are given to the six IGBT switches of bridge inverter.

Figure 12: SVPWM output gate pulses

When SVPWM pulse generator is connected to 3-phase bridge inverter with the induction motor load form a open loop drive. The motor will run at a reference speed. The reference speed

command is converted into frequency command and given to SVPWM block. The SVPWM block generates gate pulses with respect to speed command so as to run motor at reference speed.

The reference speed and motor speed graph with time and load torque=0 are as shown in below figure.

Figure 13:Open Loop Drive Speed response with TL=0

Speed response of Induction motor with different load torque is as shown in below Fig. For 1400rpm of constant input speed command and different load torque at different instant has been applied therefore the speed of motor will falls as load increases. In open loop model, variation of speed with the load is as shown in table (3)

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Figure 14: Open Loop Drive Speed response with different TL

Figure 15: SPWM based open loop drive Load Current THD

Table 3, variation of motor speed and load current response in gives the open loop model with different load torque. Also table 4, shows closed loop response with different load torques.

Table (3): Open Loop Model Variation of motor speed with Load torque

S. No. Load Torque TL (N-m)

Speed (rpm) SVPWM

Load Current (Amps)

1. 0 1391 1.5

2. 5 1374 2.1

3. 9 1359 5.3

4. 11 1352 6.4

Table (4): Open Loop Model Variation of motor speed with Load torque

S. No.

Load Torque (N-m)

Speed (rpm) SVPWM

Load Current (Amps)

1. 0 1390 1.4 2. 5 1375 1.9

3. 9 1362 5.2

4. 11 1354 6.4

ii) Closed Loop Model:

To maintain the motor speed at a reference speed value, it needs a feedback loop of motor speed and a speed controller. The drive requires a speed sensor, and the output of the speed sensor will be in terms of rpm. This speed will be processed in the speed controller as explained in the above session.

V. CONCLUSION The simulation of “Control of Induction Motor Drive Using Space Vector PWM” is carried out in MATLAB/Simulink. The simulation has been done for open loop as well as closed control. The appropriate output results are obtained. The variation of speed of Induction Motor has been observed by varying the load torque in open loop control and results are noted down in the table. Also observed that for the change in input speed commands the motor speed is settled down to its final value within 0.1sec in closed loop model.

REFERENCES:

[1] Abdelfatah Kolli, Student Member, IEEE, Olivier Béthoux, Member, IEEE, Alexandre De Bernardinis, Member, IEEE, Eric Labouré, and Gérard Coquery “Space-Vector PWM Control Synthesis for an H-Bridge Drive in Electric Vehicles” IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY, VOL. 62, NO. 6, JULY 2013. pp. 2241-2252.

[2]Mr. Sandeep N Panchal, Mr. Vishal S Sheth, Mr. Akshay A Pandya “Simulation Analysis of SVPWM Inverter Fed Induction Motor Drives” International Journal of Emerging Trends in Electrical and Electronics (IJETEE) Vol. 2, Issue. 4, April-2013. pp. 18-22 .

[3]Haoran Shi, Wei Xu, Chenghua Fu and Yao Yang. “Research on Three-phase Voltage Type PWM Rectifier System Based on SVPWM Control” Research Journal of Applied Sciences, Engineering and Technology 5(12): 3364-3371, 2013. pp. 3364-3371.

[4]K. Mounika, B. Kiran Babu, “Sinusoidal and Space Vector Pulse Width Modulation for Inverter” International Journal of Engineering Trends and Technology (IJETT) - Volume4Issue4- April 2013. pp.1012-1017.

[5]K. Vinoth Kumar, Prawin Angel Michael, Joseph P. John and Dr. S. Suresh Kumar. “Simulation And Comparison Of Spwm And Svpwm Control For Three Phase Inverter” ARPN Journal of Engineering and Applied Sciences VOL. 5, NO. 7, JULY 2010. pp. 61-74.

[6]Keliang Zhou and Danwei Wang, Member, IEEE “Relationship Between Space-Vector Modulation and Three-Phase Carrier-Based PWM: A Comprehensive Analysis” IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. 49, NO. 1, FEBRUARY 2002.pp. 186-196.

[7]Dorin O. Neacsu, “Space Vector Modulation – An Introduction” IECON’01: The Annual Conference of the IEEE Industrial Electronics Society-2001. pp. 1583-1592.

AUTHORS

Mohammed Abdul Khader Aziz Biabani is a PG student [Power Electronic &Systems] of Electrical & Electronics Engineering department, from Muffakham Jah College Of Engineering & Technology, Affiliated

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to Osmania University Hyderabad, Telangana, India. Received his B.Tech degree in Electrical & Electronics Engineering from VIF College of Engineering & Technology, Affiliated to Jawaharlal Nehru Technological University Hyderabad, Telangana, India in 2013. His research interests include Power Electronic Systems, Power Systems, Industrial Electronic Systems. His main objective is to innovate & learn new

technologies, & the scope is to fill gap between industry .

Mr Syed Mahamood Ali is a PG student [Power Electronic & Systems] of Electrical Engineering department, from Muffakham Jah College Of Engineering & Technology, Affiliated to Osmania University

Hyderabad, Telangana, India. Received his B.Tech degree in Electrical & Electronics Engineering from Jaya Prakash Narayan College Of Engineering & Technology, Affiliated to Jawaharlal Nehru Technological University Hyderabad, Telangana, India in 2013. His research interests include Power Electronic Systems, Electric Drives and Industrial Electronic Systems.

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